System for comminuting solids



y 1941- McKlNLEY STOCKTON 2,242,795

SYSTEM FOR CONMINUTING SOLIDS Filed June is, 1937 M KINLEY STOCKTON Q //v E 70/? ?atented May 20, 1941 SYSTEM FOR COMMIN'UTING SOLIDS McKinley Stockton, Redmond, reg., assignor to The Dicalite Company, Los Angeles, Calif a corporation of Delaware Applicationilune 19, 1937, Serial No. 149,187 3 Claims. (Cl. a3-94) The object of my invention is to provide new and improved means for commuting solids, particularly solids such as vdiatomaceous earth which have a fragile internal structure.

The invention comprises broadly a system in which the earth, originallyin the large lumps in which it is taken from the deposit, is cracked by wedging forces, pressure or other suitable means into lumps. of moderate size; in which a stream of the lumps is commingled with a stream of hot gases by which the earth is heated and deprived of water; in which the cooled gases and the water vapor evolved from the earth are separated from the dried lumps and discharged from the system, and in which the lumps of earth are finally, and only after substantially complete drying, introduced into'a hammer mill, fan mill or other apparatus by which they are disintegrated and reduced to a powder by repeated impacts at high velocity.

' In its preferred form the invention comprises the additional steps of an intermediate separaa tion of spent gases and water vapor from the stream of lump earth prior to the completion of. the drying thereof; the formation of the partially dried lump earth into a second stream, and the commingling of the earth stream with a second stream of hot gases to effect thedrying of the lumps prior to their disintegration by impact.

It is well known to dry diatomaceous earth-by bringing it into contact with a stream of hot gases, but heretofore this method of drying has been applied during the process of disintegration.-

For example, ,in Stockton Patent 1,611,791 a stream of hot gas is introduced into the suction of a hammer mill in which the lump earth from a a stream of hot gas is introduced into the suction of a fan mill which produces the first disintegration and a second streaminto the suction of a second fan mill in which the disintegration is completed. In bothof these cases, and regardless of the relative position of the first impact mill, it is obvious that at least the first impact disintegration is performed on an earth which is incompletely, if at all, dried, and in fact these systems subject the earth to the forceful impacts required for partial disintegration before any material quantity of water is removed from-the lumps of earth fed to them.

The advantages attending the drying of diatomaceous earth in lump form and prior to the fan mill in which the second disintegration is accomplished. Also in Cummins Patent 1,813,916

application of the pulverizationstep thereto may briefly be stated as follows:

Diatomaceous earth consists of an aggregation of the siliceous skeletons or casts of marine or lacustrine diatoms. In.crude earths of good quality these, casts, which are of microscopic size but of an elaborate structure, are in large part unbroken, and the quality of the products made from the crude depend to a great extent on the maintenance of this unbroken structure through the various manufacturing'operations and particularly through the steps of drying and pulverization. The unbroken diatom structures behave like wool fibres, felting into a mass'which is of extreme porosity and lightness and better adapted than perhaps any other known material to the filtration and clarification of liquids, while the breaking down of the diatom structures pro gressively reduces the porosity and increases the density of the mass until, when the degradation of the structures hasbeen carried to the limit, the mass of crushed particles has substantially the properties of an amorphous siliceous mass and has entirely lost its usefulness as a filtering agent and for most other purposes.

Diatomaceous earth as it occurs in 'nature is usually water saturated and the crude earth as taken from the deposit often contains or more by weight of free water. This water is strongly retained and air drying under favorable summer conditions will seldom reduce the moisture content below about 8% after 30 days exposure, while in winter drying practically ceases. The cost of handling and..;the uncertainty of result make the air drying step economically unat tractive and it is customary to dry the crude earth by the application of superatmospheric temperatures. I

The wet earth as taken from the deposit is relatively very heavy and the presence of water and often of traces of clay render it tough and even slightly plastic. Per contra, lumps of dried 'diatomaceous earth are extremely light and very brittle. Itfollows that while the wet earth may be cracked down to lumps of moderate size (as for example such as will pass through a 2"mesh screen) with relatively small damage to the diavalue of the product, while in the driedform it may be disintegratedto powder in hammer mills or fan mil-ls with much less depreciation. In the practice of. the process herein disclosed I have,

, in fact, greatly improved both the quality and the yield of the types of product used for filtration of liquids and have decreased the proportionate yield of relatively vvalueless fines or broken diatoms.

Lump diatomaceous earth has heretofore been dried prior to comminution, but only by methods each of which has serious disadvantages. Air drying is costly, uncertain, and restricly-rlz o favorable seasons and climatic conditions. ing by indirect heat, as insteam jacketed r fire heated pans, is prohibitively wasteful of' fuel.

Drying by direct contact with counterflowing fire gases, as ina rotary kiln or'on a rabbled hearth, involves the use of costly apparatus, a? heavy power consumption, and awaste of fuel due to the low firing temperature required to avoid overheating of the dried lumps which encounter the hottest gases.

I have discovered that, when certain precautions are taken in the arrangement and opersuction.

' pipe l0 having a valve or damper II to control the flow of primary air to the burning fuel. This furnace may be operated either above orbelow atmospheric pressure, as may be preferred, though in the drawing it is illustrated as operating under The gases produced by perfect combustion in the furnace may be too hot to apply to the lumps of earth and in such cases should.- be tempered by admixture with a cold or a cooler gas. Air for this purpose may be drawn into the combustion.

space of the furnace through pipe [0 or preferably may-be introduced into the gasfstream flowing ation of the apparatus, it is possible to apply the principle of. concurrent, direct contact heating to the drying of relatively large lumps of diatomaceous earth and other materials of which it is desired to preserve the internal structure through a comminuting step, and that by proceedi'ig in the manner below described I obtain a product of improved quality, in apparatus of materially reduced cost, and with a minimum consumption of fuel. These precautions will be desribed in connection with the following descriptions of exemplary apparatus suited to the practice-of the methods of the invention, these 7 descriptions referring to the attachedl'drawing which illustrates in a diagrammatic manner an assemblage of apparatus particularly adapted to the treatment of massive, compacted earths substantially free from organic matter.

Referring first to'Fig'. 1, ll is a pair'of'. toothed rolls revolving toward each other and supplied with large lumps of the earth'as taken from the deposit or as partially air dried i-fso preferred.

These rolls, or a jaw or other crusher which might be substituted for them, crack the earth into lumps of moderate size. These are conventional methods for accomplishing the first size reduction. It is desirable to exercise the least possible;

crushing effect on the wet earth, and'for this reason I prefer toothed rolls, which exercise a No' rule can be laid down for the size of the lumpsas the preferred size will depend on the propor-- wed'ging forcefirather than-jaw crushers.

tion of original waterand also the relative freedom of drying, this being in turn governed by the.

presence or absence of clay andother factors. In a general way it may be said that the crude lumps should range downwardly from a maximum of 2", though this is by no meansa limiting condition and the most favorable size range for.

any given deposit will be found only by experiment.

The cracked earth may conveniently be caused to fall on a tilting apron 2 by which it is di-- verted into one or the other of the lump storage bins 3--3, from one or the other of which a continuous stream of the lumps is delivered on to a.

belt conveyor 4 by means of'any feeding device indicated at 5+5. The conveyor delivers this 1 stream of earth into a hopper 6 which is provided with a seal valve, indicated at I; for delivering the earth into the drying system while preventing inflow or outflow of air or gas.

A combustion chamber or furnace 8 is provided with a gas, oil, or other burner 9 and an air inlet through the furnace outlet by means'of branch pipe I2 controlled by valve I3.

The hot gaseous mixture, brought to the optimum temperature hereinafter defined, enters the drying tube M where it encounters the stream of earth passing through seal valve 1. The combined stream traverses the length of tube H, in

which interchange of heat between the gases and v the earth is effected, and enters a cyclone or other separator iii in which the earth is collected. The

spent gas and water vapor-are removedfrom the separator through pipe l6 by means of a suction blower I! and are discharged into the atmosphere or elsewhere as may be desired.

The blower l1 provides the reduction in pressure by'which the stream of. gases and earth is drawn through the drying tube. It is fully equivalent to operate the drying system at a slight superatmospheric pressure instead of at subatmospheric as shown.

The earth collecting in separator I5 is ously discharged through a seal valve l8 into a drying tube l9 which is supplied with hot gases from combustion of fuel in, furnace 20, which may. be equipped as described in connection with furnace 8.- Air for tempering the combustion gases may if required be drawn into the furnace outlet through a pipe 2| controlled by valve. 22.

Under some conditions'the supply of fuel to furnace 20 maybe discontinued or this unit may be omitted from the system, air alone being ad-.

mitted to tube l9 as will be described.

The stream, of gases and earth traverses the length of drying tube l9, in which the interchange of heat between'the gases and the earthis effected, and'enters the suction of a fan mill 22 'in which the earth, which at this stage is substantially completely dried, is pulverized to the desired fineness, ordinarily that required in atfllter-aid.

'I'he pulverized earth, spent, gases, and water pact, as in a fan mill or hammer mill. Substantially complete drying should be interpreted as drying to the moisture content permissible in the pulverized final product, or that which renders the earth so friable that it may be disintegrated without material damage to the diatom structure. Ordinarily this will be from 3% to 8% by weight of .uncombined water, though in cases of exceptionally pure and friable earths it may be even as high as 15%.

The above degree of dessication may, under favorable conditions, be produced by the use of continuin Cummins) hot gases in only the first pass, 1. e., in drying tube M. In this case, as above said, secondary furnace 20 'is not operated and air is admitted at valve 22 only to carry the dried earth from separator I into fan mill 22'.

The drying tubes, and particularly the primary tube M, should be extended to the greatest possible length if it is desired to secure the maximum of fuel economy. In these tubes the flow of gases and earth is concurrent and the temperature head from gas to earth diminishes progressively toward the tube outlet, making heat transfer relatively slow at this end' of the tube.

economical overall adjustment of the system is usually that in which the greatest possible proportion of the total water is removed in the first stage, even though this entails a moderate increase in temperature at the outlet of the primary tube.

It will be understood that the temperatures above recited are suggestive only and not limiting,

The lengths of the tubes are minimized in the drawing. In practice they are proportioned to the quantity of water to be evaporated, the volume of gas per pound of earth fed, the permissible initial temperature of the gas and the velocity of the gas stream,

\ Because the earth first encounters the hot gases while in the wet condition and in the form of lumps substantially free from fine particles, it

and that they will be modified in the light of experience with difierent earths and under varying conditions.

The dried material finally entering fan mill 22 for disintegration still consists mainly of lumps, though these will usually be of smaller average size than those originally supplied to the primary drying tube. This reduction in average size is due mainly to cracking and spalling of the larger original pieces during drying, though some dust is is possible to utilize gases at a much higher ini- I tial. temperature than is possible either in countercurrent heating (as in a rotary kiln or on a hearth) or where the gas is-introduced into the disintegrating device (as inStockton 1,611,791 or The rapid evaporation of water from the surface of the lump and 'the simultaneous diffusion of water from the interior or the exterior portions efiectively protect the superficial portions of the lump from overheating until a considerable-part of the water has been evaporated, at which time the gases have cooled below 7 the danger point. It is therefore possible to supply primary drying tube M with extremely hot gases, as of the order of 1800 to 2000 F... such as have heretofore been used only for the calcina-= tion of previously pulverized earth. These initial temperatures may be used without the slightest danger of glazing or sintering the surfaces of the lumps.

With 'sufiicient extension of the primary dry-. ing tube it is possible to reduce the dischargedgas-vapor mixture to 200 or even to 150 F. Evaporation of water from the earth continues down to these low temperatures because of the high ratio of fixed gas towater vapor even at the outlet end of the tube. Because of this wide range between initial and final temperatures and be cause of the small spreadbetween final temperature and atmosphere, this stage of the process is extremely economical of fuel, requiring but little more heat supply than that rendered latent in evaporating the water. i

In some cases, as for instance where the water percentage is excessive or the water is strongly retained because of clay or gelatinous silica in the earth, it may be impossible to dry to the required final percentage in the primary tube alone without unduly reducing its throughput. In such cases I the hot gases for drying are introduced directly I utilize theseconda'ry drying stage above de-.

scribed, supplying hot gases to secondary drying tube l9; As the earth entering this stageis much reduced in water content, it is advisable to maintain the hot gas supply at a materially lower initial temperature, as for example from 800 to 1000 F. The second drying stage discharges its vent gas at a higher temperature than the first stage and is necessarily less economical of fuel, but by reason of replacing the gas-vapor mixture existing at the tail end of thefirst stage with a dry gas at a higher temperature, a relatively small hot gas supply will complete the dessication of a large quantity of partially dried earth. The most formed and is vented from the separators with the spent gases. This dust may be collected in a bag-house or spray tower if it should constitute a nuisance. The amount of actual pulverization tia, but the fragility imparted to the lump by the removal of water (fragility of the lump as a whole, notof its constituent diatom structures) more than offsets this reduction in distintegratmg force. The methods and apparatus above described thus render possible the retention of an increased proportion of the diatom structures in the unbroken condition, and correspondingly in= creasethe value of the comminuted product while decreasing the cost of apparatus and the consumption of power and fuel. a

The very striking advantages attending the use of the above described methods and apparatus are shown by the following figures for wet density of the comminuted product, for fiow rate in filtering raw sugar solutions and for clarity of the filtrate. The first columnshows the test figures for an earth milled in the manner shown in Fig. 1 of my U. S. Patent 1,611,791, in which into the suction of the mill in which the first comminution is effected. The second column shows the results with identical crude earth (and equal doses in the filtration tests) when-dried and comminuted in the manner above described.

Old method New method Wet de'nsity 19.5 15.2 Flow rate 228 458 Clarity G- v v H As will be seen, the density of the comminuted earth is reduced 22%, while for equal clarities the flow rate is almost exactly doubled. These are major advantages.

. I claim as my invention:

1. The method of drying and comminuting crude diatomaceousearth which comprises: feeding lumps of said earth into a rapidly moving stream of hot fixed gases; maintaining said lumps and said gases in direct contact and in motion in a common substantially horizontaldhrection until a desired proportion of the water content ha'sbeen vaporized from said lumps; separating the partially dried lumps from said gas stream and rejecting said gas stream; feeding said separated lumps into asecond rapidly moving stream of hot fixed gases? maintaining said lumps in direct contact with'said second stream and in motion in a common substantially horizontal direction until said lumps are substantially completely dried, andpulverizing said lumps only after last said drying step.

2. The method of drying and comminuting crude diatomaceou's earth which comprises: feeding lumps of said earth into a rapidly moving stream of hot fixed gases; maintaining said lumps and said gases ,in direct contact and in motion in a commonsubstantially horizontal direction .until said lumps of earth are substantially completely dried; separating said lumps from spent gases and vapors and diverting said gases and vapors out of the system; suspending said lumps in a second gaseous). stream, and pulverizing said lumps by repeated impacts while in suspension in said second stream and only after the completion of 

